hyodae seo woods hole oceanographic institution art miller, aneesh … · 2013-10-28 ·...
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Predictability and Coupled Dynamics of MJO during DYNAMO:Role of diurnal SST in the initiation and intensity of the “MJO2”
ONR LASP & HIRES DRI Peer ReviewSeptember 25, 2013
Hyodae SeoWoods Hole Oceanographic Institution
Art Miller, Aneesh Subramanian, Nick CavanaughScripps Institution of Oceanography
Project’s Overall Goal
• To investigate the coupled boundary layer process and predictability of MJO
• Global coupled modeling component (Miller, SIO)
• NCAR CCSM4 featuring realistic MJOs (Dr. Aneesh Subramanian)
• MJO diagnostics in the present and warming climate (Dr. Aneesh Subramanian)
• Linear inverse modeling (Mr. Nick Cavanaugh)
• Regional coupled modeling component (Seo, WHOI)
• Construct a skillful regional O-A model for DYNAMO
• Process-model to test the effect of coupled boundary layer process
• Diurnal cycle in SST and barrier layer ↔ MJO convection
Scripps Coupled Ocean-Atmosphere Regional (SCOAR) ModelVERSION II
• Originally coupled RSM-ROMS in the tropical Pacific, Indian and Atlantic Oceans (Seo et al. 2007, J. Climate).
• Study mesoscale ocean-atmosphere interactions and large-scale climate.
• An input-output-based coupler
• WRF-ROMS coupling
• WRF and ROMS are coupled in the tropical channel configuration.
• Matching horizontal grids at 40 km.
Flux-SST Coupler
1. Weather Research and Forecasting
Model (WRF)
2. ScrippsRegional Spectral
Model (RSM)
Regional Ocean
Modeling System (ROMS)
SCOAR Model
SST, Current
Atmospheric Forcing
Atmosphere Ocean
Lateral Boundary Conditions: IPCC models, reanalyses
MJO diagnostics from multi-year SCOAR2 simulation
6-month integration (October to March) for 5 winters 2005-2006 to 2009-2010
Daily coupled (CF=24)ROMS: HYCOM daily ocean analysis
WRF: ERA-Interim 6-hourly reanalysis
Wavenumber-frequency spectra of symmetric component of OLR and U10m, 10S-10N
wavenumber wavenumber
freq
uenc
yfr
eque
ncy
wavenumber
SCOAR2 OLRSatellite OLR SCOAR2_No_Coupling OLR
SCOAR2 U10mNCEP U10m SCOAR2_No_Coupling U10m
30-80 day, k=1~3
peri
od [
day]
peri
od [
day]
Effect of diurnal SST coupling in SCOAR for intensity of convection of MJO2 during DYNAMO
Experiments for MJO2 during DYNAMO:Test the effect of diurnal SST on the MJO2 convection
• Vertical levels: a large number of vertical levels in the upper ocean (e.g, Bernie et al. 2008, Klingaman et al. 2011)• Total # of levels: 55 layers• 5 layers in the upper 1 meter• 15 in the upper 15 meters
• Simulation Period: MJO2 period• One month, Nov. 14 - Dec. 14, 2012
• Initial and boundary conditions: • ROMS: HYCOM daily ocean analysis• WRF: ERA-Interim 6-hourly reanalysis
• Coupling frequency (CF): Different CFs applied to otherwise identical SCOAR2 runs.• CF=1, 3, 6, 24 hours
• Ensemble simulation: 5-member in each case
Rainfall time-series averaged over NSA
Evolution of MJO2 precipitation with different coupling frequencies10S-10N mean precipitation rates
• Observations: MJO2 rainfall event on Nov. 24 with the eastward propagation at 5 ms-1.
• Models: qualitatively consistent intraseasonal evolution of rainfall.
• With more frequent coupling, the higher amount of rainfall is achieved during the active phase of convection.Why does it rain more with higher frequency coupling?
Pre-convection Mid-convectionaverage of 73-80.5°E, 0.7°S-17°N
Along-track evolution of the upper ocean temperature at the Revelle
• The upper ocean warms during the suppressed phase of MJO (recharge phase)
• Pronounced diurnal variation in SST reaching >0.7C.• The peak warming is greater with stronger diurnal cycle.• Diurnal warm layer up to 3 meters.
Revelle temp. anom. Model temp. anom.
CF6
CF24
CF1
• Large diurnal variations help achieve higher SST values on diurnal time-scales during the suppressed phase.
Mean/STD Mean/STD
Spatial patterns in diurnal amplitude in SST
• Larger diurnal amplitude in SST during the pre-convection period.
• Higher coupling frequency allows greater amplitude of diurnal SST amplitude.
• Reduced diurnal cycle during the mid-convection period
Pre-convection Mid-convection
CF3
CF1
CF6
Spatial patterns in diurnal amplitude in SST
• Larger diurnal amplitude in SST during the pre-convection period.
• Higher coupling frequency allows greater diurnal SST amplitude.
• Diurnal warm layer eroded by wind during the convection
CF1
CF3
Pre-convection Mid-convection
CF6
What is the implication to the
convection?
Evolution of specific humidity
•The recharge period is characterized by drying of the atmosphere column.
• A gradual moistening of the atmosphere from Nov. 18 in ERA-Interim and models.
• The peak moistening on Nov. 24, coincident to the deep convection and the maximum rainfall.
• The extent to which the atmosphere is moistened is greater in CF1 than CF24.
• The mean specific humidity profiles suggests that the atmospheric column becomes moister with higher frequency coupling.
CF1
CF24
ERA-I
Q anomalyQ Mean
Why increased rainfall during the active phase of MJO with higher coupling frequency?
Column integrated Moist Static Energy (MSE) budget analysis
MSE Budget over the Northern DYNAMO region
Maloney 2009
m = cpT + gz+ Lqmt
tendency
= − vh ⋅∇mhorizontaladvection
− ωmp
verticaladvection
+ LH + SH( )
latent+sensibleflux
+ LW + SW
long+shortwaveflux
Recharge of MSE Dominant role by LH for MSE recharge
Vertical advection of MSEis a dominant export term
LH+SH, and LW+SW
source of MSE
MSE budget terms prior to the MJO2
MSE budget terms during the MJO2
+R
• MJO suppressed phase• Recharge of MSE by LH.• A buildup of MSE is “faster” with higher coupling frequency, associated with stronger import by LH and export by LW.(Maloney et al. 2010; Sobel et al. 2008)
MSE Budget over the Northern DYNAMO region
Maloney 2009
m = cpT + gz+ Lq
• MJO suppressed phase• Recharge of MSE by LH.• A buildup of MSE is “faster” with higher coupling frequency, associated with stronger import by LH and weaker LW export by LW.(Maloney et al. 2010; Sobel et al. 2008)• MJO active phase• LH+SH and LW+SW continue to be the major source terms of MSE.• Vertical advection by deep convection is a dominant export process.• Stronger vertical advection with more frequent coupling!
mt
tendency
= − vh ⋅∇mhorizontaladvection
− ωmp
verticaladvection
+ LH + SH( )
latent+sensibleflux
+ LW + SW
long+shortwaveflux
Recharge of MSE Dominant role by LH for MSE recharge
Vertical advection of MSEis a dominant export term
LH+SH, and LW+SW
source of MSE
MSE budget terms prior to the MJO2
MSE budget terms during the MJO2
+R
+R
Overall linear lead-lag relationship between SST and rainfall
• Higher CF leads to warmer SST during the suppressed phase.
• This leads to higher rainfall amount during the active phase.
• Heat and moisture flux feedback associated with warmer SST responsible for the intensity of convection (Arnold et al. 2013)
� Ensemble averages• Individual members
Summary
• SCOAR2 supports significant eastward propagating convectively coupled disturbances in the MJO wavenumber-frequency band.
• Improved representation of diurnal cycle leads to higher SST during the suppressed phase of convection.
• LH plays an critical role in a rapid recharge of MSE.
• A buildup of MSE pre-conditions the deep convection, followed by intense precipitation during the active phase of MJO.
• Consistent with the recharge-discharge paradigm of Blade and Hartmann (1993).
• We found a quasi-linear relation in this recharge-discharge process to the frequency of coupling in a regional coupled model.